i am new on using EMS, and i have problem with segmentation

i want to do the example that is on EMS site with BrainWeb images
and i did all the steps according to the guide but when i want to do the
segmentation, i see this error

Calculating classification      ??? Error using ==> schur
NaN or Inf prevents convergence.

Error in ==> sqrtm at 33
[Q, T] = schur(A,'complex'); % T is complex Schur form.

Error in ==> ems_segment at 659
        mahalanobis_sq = (planeCorrectedData -
ones(size(playingInd))*means(:,class)') / ...

Error in ==> ems_segment>uiForEms_segment at 846
    ems_segment(dataNames, use2D, maxBiasOrder, useMRF, ...

Error in ==> ems_segment at 90
uiForEms_segment

??? Error while evaluating uicontrol Callback.

and i couldn't understand why this hap! pen!
i checked for the other image but i have te same problem,

can anyone help me?

Kind Regards
kamran